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hduregger
Journeyman III

Where does factor 2 in peak GFLOPS calculation come from?

I am looking at the programming guide and the ISA manual but I just can't figure out where the additional factor 2 comes from.

e.g. for the 6970 the peak is given as StreamCores * ALUs * EngineSpeed * 2 / 1000 = ProcessingElements * EngineSpeed * 2 / 1000 = 384 * 4 * 880 MHz * 2 / 1000 = 1536 * 880 MHz * 2 / 1000 = 2703.36 GFLOPS. I thought I would understand the architecture quite well by now. But that factor 2 keeps me puzzled.

Others on these forums also included that factor in their computations.

Can someone please give me a hint where it comes from?

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maximmoroz
Journeyman III

MULADD instruction takes 1 cycle to execute and does 2 operations: 1 multiplication and 1 addition.

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Ah, right, of course, it's that easy to understand, haha. My brain somehow masked that possiblity because I thought that operation must be too costly, even while looking over Table 4.14. Never take something for granted.

Thank you maximmoroz!

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